Method of forming microchannel plates having curved microchannels

ABSTRACT

A profiled microchannel plate is obtained from a bundle which is formed from monolayers of microchannels. These channels are adjacently arranged and have the same curvature which is obtained by the profiling of each monolayer. The microchannel plate is obtained by cutting such a channel bundle into segments along mutually parallel planes which, however, are not parallel to the longitudinal direction of the channels.

Polaert May 13, 1975 [54] METHOD OF FORMING MICROCHANNEL 3,331,670 7/1967 C016 65/4 PLATES HAVING CURVED 3,461,332 8/1969 Sheldon 313/105 X 3,558,377 1/1971 Tantillo 65/4 X MICROCHANNELS 3,594,457 7/1971 Wright 65/DIG. 7 [75] lnventor; Re'my Hem-i Francois Pulaert, 3,669,639 6/1972 lnoue et al 65/4 villecresnes France Siegmund [73] Assignee: U.S. Philips Corporation, New York, NY. Primary ExaminerRoy Lake Assistant Examiner.l. W. Davie [22] Flled' May 1973 Attorney, Agent, or FirmFrank R. Trifari Appl. No.: 361,287

[30] Foreign Application Priority Data 1 1 ABSTRACT 7 May l9 2 France 72 18043 A profiled microchannel plate is obtained from a bun- [52] Us Cl 65/4, H05, 65/44 dle which is formed from monolayers of microchan- [5 I] (303C1 23/20 nels. These channels are adjacently arranged and have [58] Fieid 17 25 '8 the same curvature which is obtained by the profiling 29/592. 5. 6 6 of each monolayer. The microchannel plate is ob- 36 I 1 I tained by cutting such a channel bundle into segments along mutually parallel planes which. however, are not [56] References Cited parallel to the longitudinal direction of the channels.

UNITED STATES PATENTS 9 Claims 5 Drawing Figures 3,244,922 4/1966 Wolfgang 313/105 X PATENTEB .lIalllll Fig,5

1 METHOD OF FORMING MICROCHANNEL PLATES HAVING CURVED MICROCHANNELS The invention relates to a secondary emissive electrode for electron tubes, and to a method of manufacturing such an electrode. This electrode comprises microchannels, extending between an entrance face and an exit face, on the inner surfaces of which secondary electron emission occurs with an emission coefficient which is larger than 1 as a result of the application of a potential difference between said faces. The invention relates in particular to electrodes having curved channels. The curvature of the channels reduces, on the one hand, the parasitic electron emission and radiation which is due to the known ion feedback phenomenon and, on the other hand, the transmission of stray light through the microchannels.

Electr des comprising curved microchannels are described inter alia in US. Pat. No. 3,461,332. This patent specification describes an electrode of the kind set forth, but it does not describe a method of realizing the curvature of the microchannels. This patent teaches many different constructions for the fibers. For example, at col. 4, lines 25-32, fibers are described having a core of one kind of glass and a coating of another kind of glass. These fibers are then fused together by heating and the glass cores subsequently etched out without attacking the glass coating.

Methods of forming such electrodes are described in French Pat. No. 2,1 16,913 granted July 21, 1972, and in US. Pat. No. 3,838,996 granted Oct. 1, 1974, both in the name of Applicant. The method described in French Pat. No. 2,1 16,913 consists in the formation of a given bundle of fibres of the type used to form microchannel plates, the ends of said bundle being arranged in two clamps, one of which is fixed whilst the other is vertically and horizontally displaceable or is capable of performing a rotary movement about the axis of the bundle. The said bundle is subsequently heated between the two clamps to the softening temperature of the glass, after which the clamps are displaced with respect to each other. The desired curved channel plate is subsequently cut from the part of the fibre bundle thus distorted. One of the drawbacks of such a method is that a comparatively large quantity of material in the form of a fiber bundle is required, a substantial part of which is lost after bending and cutting. Another drawback of the said method is that the curvature of the channels in the plate thus obtained is not the same everywhere; this is due to the fact that the distortion at the centre of the bundle is not the same as that on its circumference.

According to the method described in US. Pat. No. 3,838,996, the operations are performed on a preformed microchannel plate. The quantity of material lost is thus substantially reduced. The channel plate is subjected to a mechanical stress which engages at an angle with respect to the end faces of the plate. In the interior of the said plate, the planes which are parallel to the said end faces are isothermal, whilst, at least in a part of the plate, measured along the normal to the end faces of the plate, the temperature varies and therewith the glass on this traject may vary between the plastic phase and the elastic phase. This method requires the manufacture of a special holder in order to apply the said mechanical stress. This holder consists, for example, of a die which is composed of two parts,

the shape of which corresponds to that of the channel plate, a given clearance existing between said parts in order to allow displacement with respect to each other. A difficulty in said method is how to obtain the same curvature for all micro-channels of the plate. The method requires a geometry of the edges of the die such as to prevent barrel-like distortion of the plate due to the bending of the microchannels situated on the periphery under the influence of the mechanical stress. The means used to apply the mechanical stress can also be formed by two end pieces, each of which is fused to one of the end faces of the plate. A difficulty in this respect is that the mechanical and thermal properties of the material used for these end pieces must be adapted to the conditions in which the fibre material exists when the mechanical stress is applied.

The difficulties encountered in performing said method are due to the fact that the basic material already has the dimensions of a channel plate, so that a given curvature must be imparted to a large number of adjoining microchannels.

In accordance with the method according to the invention, the uniformity of the curvature can be obtained in a more reliable and simpler manner as a result of the fact that this curvature is uniformly imparted to a series of sub-elements which are subsequently assembled in a compact form so as to obtain a channel bundle of large cross-section from which the microchannel plates are cut.

The method is particularly suitable for microchannels having a square or a rectangular cross-section. These channels are adjacently arranged without clearance there between. The curvature of the channels is obtained by subsequently applying a shearing force in a direction transverse to the longitudinal direction of the channels.

According to the invention, a secondary electron emissive electrode of the microchannel plate type is composed of a stack of microchannel layers, the curvature in the axial direction of adjacently arranged channels being the same, and extending in the same direction.

The invention also relates to a method of manufacturing such an electrode. According to this method, straight microchannels of the same cross-section are adjacently arranged in order to form a layer, this layer being subsequently arranged between two clamping jigs, each jig having a ribbed profile which can engage in that of the other jig, the ribs being directed perpendicular to the axes of the microchannels, the layer being distorted under the influence of a force which is exerted on said jigs in a direction transverse to the microchannel layer, whilst the layers which are thus profiled are subsequently stacked to form a compact unit by thermal treatment, after which curved microchannel plates are cut from the stack thus obtained along planes which are not parallel to the longitudinal axes of the microchannels.

The method according to the invention is suitable for microchannels having inter alia circular, square, rectangular or polygonal cross-section, a maximum fill rate of the microchannels of the plate being attainable, for example, in the case of a rectangular, triangular or hexagonal cross-section.

A preferred embodiment of the method according to the invention is adapted to bulk manufacture. A plural- 3 ity of microchannel layers are then simultaneously profiled.

Some preferred embodiments according to the invention will be described in detail hereinafter with reference to the drawing.

FIG. 1 shows a layer of adjacently arranged micro channels (monolayer).

FIG. 2 shows a preferred embodiment of a clamping jig to be used for clamping the monolayer during profilmg.

FIG. 3 is a side elevation of a device for the profiling of such a layer.

FIG. 4 shows a plurality of stacked and profiled monolayers.

FIG. 5 shows a diagram of a method of simultaneously profiling a plurality of such microchannel monolayers.

For the sake of clarity, the figures show only microchannels having a square cross-section. However, the invention obviously also relates to microchannels having an arbitrary other cross-section.

The letter P in FIG. I denotes a surface on which identical microchannels I], having a cross-section 12, the specific structure of which is not shown because the specific structure is not relevant to the present inven tion, are adjacently arranged so as to form a monolayer I. Each microchannel II can also be replaced by a small number of microchannels which are combined to form a compact bundle which also has a square crosssection.

FIG. 2 shows a clamping jig 20, for example, made of stainless steel. One of the surfaces of this clamping jig is provided with a succession of parallel ribs and recesses which are alternately arranged in two parallel planes. The ribs 21, 23 and 25 are situated, for example, in one common plane, whilst the recesses 22, 24 and 26 are situated in a different common plane. The ribs and recesses are separated by inclined surfaces, for example, the surface 27, the angle between each surface 27 and the normal to the said ribs and recesses being the same.

In accordance with the method according to the m vention, the surfaces of the clamping jigs which are provided with the said profile are arranged opposite to each other, as is shown in FIG. 3.

The said clamping jigs 30 and 31 ara arranged at a given distance from each other, both profiles being parallel to each other: these profiles can engage in each other when one of the clamping jigs is displaced in the direction transverse to the plane of the profiles.

A layer of microchannels is arranged between said clamping jibs as is shown in FIG. 1. Under the influence of a force C, directed transverse to the outer surfaces 32 and 33 ofthe clamping jigs 30 and 31, a given distortion is imparted to the monolayer l. The compression is preferably performed under the following circumstances:

using heating means which are not shown in the figure, the temperature of the monolayer I is raised to a value such that its material (glass) assumes a phase between the plastic phase and the elastic phase;

the clamping jigs are made of a material which does not readily oxidize during the treatment, for example, stainless steel covered with a layer of tungsten carbide. As a result, the material of the channels does not adhere to the clamping jigs;

- the compression is effected under vacuum or in a reducing atmosphere in order to minimize the risk of oxidation of the metal during the treatment;

the said heating means are preferably formed by 5 the clamping jigs themselves which can be pro vided with electrical heating elements for this purpose.

When the usual types of glass are used for the microchannel walls, the temperature at which the said treatment takes place is, for example, approximately 500 C.

The profiling can be combined with the fusing of the glass fibres of the monolayer.

To this end, one of the edges of the microchannel layer, for example, the edge 33 is arranged to be flush with a side face of the jigs against a flat abutment 34, which is connected to the clamping jig 31 at the points 35, 36 and 37 as shown in FIG. 3. When, in addition, the force C is directed at an angle which is not 90 with respect to the plane of the monolayer, the force will have a component in the plane of the monolayer such that the elements of the monolayer are pressed against the abutment 34.

After the treatment of a given number of layers, a stack of layers 41, 42, 43 thus profiled is formed as is shown in FIG. 4.

These layers are fused to each other by a thermal pressure treatment between two clampingjigs of a type similar to the clamping jigs 30 and 31 of FIG. 3.

After the formation of said stack and the thermal pressure treatment, curved microchannel plates are obtained by cutting pieces from this stack, preferably in a direction transverse to the longitudinal direction of the microchannels, for example, along the lines 40 and 50 shown in FIG. 4.

A preferred method according to the invention enables bulk manufacture of curved microchannel plates by the simultaneous profiling of a plurality of monolayers.

As is shown in FIG. 5, a stack of alternately a monolayer 1 and a separating element 51 is arranged between the clampingjigs 30 and 31. The separating element 51 is made, for example, of stainless steel covered with a layer of tungsten carbide so as to prevent adhesion of the glass. This assembly is subjected to compression between the said clamping jigs.

Each of the main surfaces of the separating element 51 has the same profile as the clamping jig which it faces. A number of monolayers is thus profiled simultaneously.

In the above method clamping jigs are used which are each provided on a main surface with a succession of alternating ribs and recesses. It is obvious that the invention also relates to the case where one of the main surfaces of each clamping jig has an arbitrary other profile, the profile of a first clamping jig engaging in the profile of a second clamping jig.

For the simultaneous profiling of a plurality of layers the profile of the separating elements to be arranged between the monolayers can be adapted to the relevant profile of the clamping jigs.

What is claimed is:

1. A method of forming microchannel plates having curved microchannels extending between major faces thereof, for use in making secondary emissive electrodes, comprising the steps of:

forming a layer of substantially straight adjacent and parallel microchannels of the same cross-section, said layer being one microchannel thick;

positioning said layer between a first jig having parallel ribs and a second jig having ribs parallel to but positioned for interdigitation with said ribs of said first jig, with said microchannels crossing said ribs;

at a temperature where said microchannels are between their plastic phase and their elastic phase, pressing said jigs toward each other to shape said microchannel layer to the contour of said jigs;

bonding said microchannels of said layer together;

stacking a multiplicity of similar so shaped and bonded microchannel layers;

bonding said stacked microchannel layers together;

and

cutting said bonded stack of microchannel layers into plates along planes which intercept said microchannels of said bonded stack of microchannel layers.

2. A method as defined in claim 1 wherein said layer is positioned between said jigs with said microchannels perpendicular to said ribs.

3. A method as defined in claim I wherein said layer is prevented during said pressing step from increasing its dimension in the direction perpendicular to the axes of the microchannels of said layer.

4. A method as defined in claim 1 wherein said microchannels are between their plastic phase and their elastic phase at an elevated temperature and said microchannels are brought to said elevated temperature by suitably heating at least one of said jigs.

5. A method as defined in claim I wherein said step of bonding said microchannels of said layer together is performed by pressure bonding said microchannels of said layer together simultaneously with the shaping thereof in the pressing step.

6. A method as defined in claim I wherein said stacked microchannel layers are bonded together by pressure bonding thereof between said ribbed jigs.

7. A method as defined in claim 1 wherein said planes along which said bonded stack is cut are parallel planes.

8. A method as defined in claim 7 wherein said planes are perpendicular to the axes of said microchannels.

9. A method as defined in claim 8 wherein said layer is positioned between said jigs with said microchannels perpendicular to said ribs. 

1. A method of forming microchannel plates having curved microchannels extending between major faces thereof, for use in making secondary emissive electrodes, comprising the steps of: forming a layer of substantially straight adjacent and parallel microchannels of the same cross-section, said layer being one microchannel thick; positioning said layer between a first jig having parallel ribs and a second jig having ribs parallel to but positioned for interdigitation with said ribs of said first jig, with said microchannels crossing said ribs; at a temperature where said microchannels are between their plastic phase and their elastic phase, pressing said jigs toward each other to shape said microchannel layer to the contour of said jigs; bonding said microchannels of said layer together; stacking a multiplicity of similar so shaped and bonded microchannel layers; bonding said stacked microchannel layers together; and cutting said bonded stack of microchannel layers into plates along planes which intercept said microchannels of said bonded stack of microchannel layers.
 2. A method as defined in claim 1 wherein said layer is positioned between said jigs with said microchannels perpendicular to said ribs.
 3. A method as defined in claim 1 wherein said layer is prevented during said pressing step from increasing its dimension in the direction perpendicular to the axes of the microchannels of said layer.
 4. A method as defined in claim 1 wherein said microchannels are between their plastic phase and their elastic phase at an elevated temperature and said microchannels are brought to said elevated temperature by suitably heating at least one of said jigs.
 5. A method as defined in claim 1 wherein said step of bonding said microchannels of said layer together is performed by pressure bonding said microchannels of said layer together simultaneously with the shaping thereof in the pressing step.
 6. A method as defined in claim 1 wherein said stacked microchannel layers are bonded together by pressure bonding thereof between said ribbed jigs.
 7. A method as defined in claim 1 wherein said planes along which said bonded stack is cut are parallel planes.
 8. A method as defined in claim 7 wherein said planes are perpendicular to the axes of said microchannels.
 9. A method as defined in claim 8 wherein said layer is positioned between said jigs with said microchannels perpendicular to said ribs. 